1. Field of the Invention
The present invention relates to an improvement in liquid and gaseous corrosion resistance and plasma resistance, which is made to the vacuum chamber and its parts formed from anodized aluminum alloy for dry etching apparatus, CVD apparatus, PVD apparatus, ion implantation apparatus, sputtering apparatus, etc. which are used to fabricate semiconductor and liquid crystal devices.
2. Description of the Related Art
The vacuum chamber for CVD apparatus, PVD apparatus, dry etching apparatus, etc. is required to have resistance to corrosion by corrosive gas (referred to as gaseous corrosion resistance hereinafter) because it is exposed to corrosive gases introduced thereinto, such as reaction gas, etching gas, and cleaning gas, which contain halogens like Cl, F, and Br. Moreover, the vacuum chamber is also required to have resistance to plasma (referred to as plasma resistance hereinafter) because it is often exposed to halogen-based plasma, which is generated therein, in addition to corrosive gases. The vacuum chamber adopted recently in the field of this application is one which is made of aluminum or aluminum alloy which is light in weight and superior in thermal conductivity.
Unfortunately, aluminum or aluminum alloy does not have satisfactory corrosive gas resistance and plasma resistance. So, there have been proposed several techniques for surface modification to improve such characteristic properties.
According to one of the proposed techniques, improvement in corrosive gas resistance and plasma resistance is achieved by forming an anodized film (0.5–20 μm thick) and subsequently heat-drying it at 100–150° C. in a vacuum, thereby evaporating and removing moisture adsorbed thereto. (See Japanese Patent Publication No. 53870/1993.) Another proposed technique involves anodization of aluminum alloy containing 0.05–4.0% of copper in an electrolyte of oxalic acid, said anodization being continued with a decreased voltage. (See Japanese Patent Laid-open No. 72098/1991.)
These techniques disclosed so far give aluminum alloy suitable for vacuum chamber components superior in gaseous corrosion resistance and plasma resistance. However, such vacuum chamber components are still subject to corrosion at the time of maintenance by wiping or washing with water, because water reacts with halogen compounds sticking to the surface of the aluminum alloy, thereby forming an acidic solution, which corrodes the anodized film. In other words, they are insufficient in resistance to acidic solution (referred to as liquid corrosion resistance hereinafter.) In addition, CVD apparatus, PVD apparatus, dry etching apparatus, etc. have some members which hold semiconductor wafers or LC glass substrates and remain in the apparatus while wafers or substrates are being washed. Such members are subject to corrosion because surface modification by conventional technologies does not protect the anodized film from corrosion by acidic solution used for washing. Corrosion on the vacuum chamber components of aluminum alloy used for fabrication of semiconductor and liquid crystal devices results in local change in their electrical properties, which deteriorates uniform processing. Thus, conventional vacuum chamber components are not suitable for the application area in which stringent electrical properties are required.
Several techniques for solution to this problem have been proposed. The first one is by treating the anodized film with fluorine. (See U.S. Pat. No. 5,069,938.) The second one is by filling pores in the anodized film with a metal salt. (See EP application No. 0648866.) The third one is by covering the anodized film with a silicon film. (See U.S. Pat. No. 5,494,713.) These techniques improve liquid corrosion resistance to some extent but do not sufficiently improve gaseous corrosion resistance and plasma resistance. Therefore, they find only limited use. Moreover, they are complicated and hence expensive and unacceptable to general use. The recent technical advance requires aluminum alloy members with improved corrosion resistance.